The work proposed for the coming year is: (1) to study the temporal sequence of the uptake of horseradish peroxidases during sustained transmitter release from reticulospinal axons in lamprey; (2) to characterize the effects of guanidine upon transmitter release from motor nerve terminals at the frog neuromuscular junction; (3) to characterize the effects of guanidine upon the excitability of reticulospinal neurons in lamprey spinal cord; (4) to examine "ephaptic transmission" between giant axons in lamprey spinal cord in solutions containing low divalent ion concentration; (5) to examine the synaptic activation of Muller cell bodies in lamprey brain produced by stimulation of single trigeminal sensory neurons. BIBLIOGRAPHIC REFERENCES: Wickelgren, Warren O. (1975). Structural presynaptic changes following repetitive action potential activity in giant reticulospinal axons of lamprey. Neuroscience Abstracts, Society for Neuroscience Annual Meeting, New York City, 1975 (Abstract). Wickelgren, Warren O. (1975). Habituation and dishabituation of synaptic responses in reticulospinal cells of lamprey. The Physiologist, 18, No. 3, August 1975. (Abstract).